Steering Geometry : Design about an inch of trail from the steering axis to the tire/road contact patch. Let desired Trail and Head Angle lead you to a required fork Offset (rake).

Chain Line: The Straighter and simpler, the better, especially on the tension side.

Parts and fasteners:

Rear Coaster brake wheels ease the dilemma of how to attach rear brake.
Self tapping screws, lag bolts, and bolts are removable and therefore allow adjustment.
Glue is more permanent, useful when you've got the design dialed in and road tested. I would probably use glue more often were it not for my commitment issues. U Bolts and hose-clamps for ease of temporary connection

Where to find resources:

Dumpsters (especially around the dorms and apartments as college lets out at the end of the quarter . ) Construction dumpsters for wood, plywood, steel conduit tubing

Along the road, At the dump, Free List, Garage Sales, (wait till its at the curb after the sale) Thrift shop and its Dumpster, Bike Shop's dumpster (lots of chain and old seats)

Can Do,
Curiosity,
Thick Skin (also helpful if you crash) ,
Thick Skull (also helpful if you crash) But always wear a helmet to protect your hair
Adventurousness, Macguyverism
Keep perspective, Treat it like a prototype not a precise piece of rocket science.
Don't Over-Analyze it (avoid "paralysis by analysis") ponder it a little then move forward anyway.
Treat it like you are building a sketch, not a masterpiece. You can always redo the sketch or learn from it to build the good one next time.

I don't put much time into making my bikes look difficult to build. I like them to look easy to build and to expose (not hide) the construction techniques.

You may find insight into the trials and triumphs the early bike inventors faced. Enjoy that. Pursue some dead ends and backwaters of the bike's evolution.

There is not much reason to build your own "normal" bike. You can get a normal bike anywhere.

Plus, you meet fun interesting folks when you ride a fun interesting bike.